Start by just going to www.twiddla.com . It'll start you a new session with it's own address. You can give that address to anybody and then they can write on there.

It was fun and easy and there was no sign-up or accounts or what-all. I figured I'd let the program speak for itself.../\ This is part of a map we made last night, with the location of the sleep-inducing plant marked by me...

Here are some more examples and explanations, click to enlarge. The first screenshot is pretty much what appears as soon as you open a Twiddla session.The arrows I drew pointing to the "draw tool" and the "grid tool" are no longer accurate since I opened the "text" tool, sorry. But they'll appear there if you hit "draw".

Epic win on this one! You can upload pictures,draw rooms quickly, and then everyone there can show how they interact. I blew an hour just doodling around on the open public sandbox. Map and picture sharing for free with no sign up wait time...Awesome! Congrats on Vornheim too!

Totally kick-ass! Now all we need is something like John Mars' die roller for DCC (http://jmarrdesign.com/dcc/roller.htm). I really like that one as you actually have to click and drag the dice to roll and it shows dice rolling instead of just numbers showing up on a line.

Yep, Google+, a die roller, and a white board would be all you would ever need.